1. Field of the Invention
This invention relates in general to a novel and improved apparatus which emits radiation, preferably for treating patients. In particular, it relates to a novel and improved apparatus for radiation therapy, preferably with accelerated electrons. More particularly, this invention is directed to a radiotherapy apparatus having light beam localizers for the projection of light beams on the surface of a body to be subjected to irradiation in order to determine the position of that surface.
2. Description of the Prior Art
From U.S. Pat. Nos. 2,204,465; 2,474,422 and 2,887,586 X-ray examination apparatus are known having arranged a mirror in the X-ray cone between the X-ray radiation source and the radiation diaphragm. The mirror is inclined by about 45.degree. to the axis of symmetry of the radiation diaphragm. This mirror projects light of a visible light source, which is arranged laterally of the mirror, through the aperture of the primary radiation diaphragm onto the surface of the object to be examined. The cone of visible light is bonded in the same manner by the diaphragm plates of the primary radiation diaphragm as the X-rays. In these so-called full field light-beam localizers, the visible light source illuminates exactly the same field which would be hit by the X-rays with the X-ray source turned on. These light-beam localizers facilitate considerably the adjustment of the X-ray radiation beam with respect to the skin area of the patient to be examined, because the illuminated field is visible on the skin surface. They are frequently also equipped with a reticle to mark the axis of symmetry of the primary radiation diaphragm on the skin surface.
From U.S. Pat. No. 3,803,418 an X-ray device for examination of skulls is known. A projector is installed in the axis of rotation about which the X-ray examination device may be rotated. A reticular light beam is radiated by the projector along the axis of rotation of the x-ray device. On the skull to be irradiated, the reticle indicates the point which lies on the axis of rotation. Of particular interest in radiation therapy, however, is the determination of the isocenter. In this respect, it is considered a disadvantage that the reticle projected on the skull of a patient is sometimes far away from the center of the disease, which is, for example, in the trunk of the body.
It is also known in radiotherapy apparatus to project a scale onto the skin surface of the patient by means of an additional projector. This scale intersects the reticle of a light-beam localizer of the radiation diaphragm. To this scale are assigned numerical values which indicate the distance of the skin surface from the focus in the intersection of the reticle of the light-beam localizer projected on the skin surface. This very practical indication device for indicating the focus-skin distance, however, can only be used for X-ray examination apparatus and for radiotherapy apparatus which work with X-rays or gamma rays. In radiotherapy apparatus which work with radiation of a lesser penetration, such as accelerated electrons, this device is not suitable, because of the absorption of the deflection mirror of the light-beam localizer which is provided in the path of rays.